﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace UgaScreenShotMaker
{
    //thanks to Stephen Toub (http://blogs.msdn.com/b/toub/archive/2006/05/03/589423.aspx)
    public class KeysHook : IDisposable
    {
        private delegate IntPtr LowLevelKeyboardProc(int nCode, IntPtr wParam, IntPtr lParam);

        #region DLLImports
        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern IntPtr SetWindowsHookEx(int idHook,
            LowLevelKeyboardProc lpfn, IntPtr hMod, uint dwThreadId);

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        private static extern bool UnhookWindowsHookEx(IntPtr hhk);

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode,
            IntPtr wParam, IntPtr lParam);

        [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern IntPtr GetModuleHandle(string lpModuleName);

        #endregion

        #region constants and variables

        private const int WH_KEYBOARD_LL = 13;
        private const int WM_KEYDOWN = 0x0100;
        private LowLevelKeyboardProc _proc;
        private IntPtr _hookID = IntPtr.Zero;

        #endregion

        public event EventHandler<EventArgs<Keys>> OnKeyDown;

        public KeysHook()
        {
             _proc = HookCallback;
        }

        public void Hook()
        {
            _hookID = SetHook(_proc);
        }

        public void Unhook()
        {
            if (_hookID != IntPtr.Zero)
            {
                UnhookWindowsHookEx(_hookID);
                _hookID = IntPtr.Zero;
            }
        }

        public void Dispose()
        {
            Unhook();
        }

        private IntPtr SetHook(LowLevelKeyboardProc proc)
        {
            using (Process curProcess = Process.GetCurrentProcess())
            using (ProcessModule curModule = curProcess.MainModule)
            {
                return SetWindowsHookEx(WH_KEYBOARD_LL, proc,
                    GetModuleHandle(curModule.ModuleName), 0);
            }
        }

        private IntPtr HookCallback(int nCode, IntPtr wParam, IntPtr lParam)
        {
            if (nCode >= 0 && wParam == (IntPtr)WM_KEYDOWN)
            {
                int vkCode = Marshal.ReadInt32(lParam);
                Keys key = ((Keys)vkCode);
                if (OnKeyDown != null)
                {
                    OnKeyDown(this, new EventArgs<Keys>(key));
                }
            }
            return CallNextHookEx(_hookID, nCode, wParam, lParam);
        }

    }
}
